The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium tetraisopropoxide [Ti(O-i-Pr)4] and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96% e.e.). A remarkable rate enhancement was brought about by the addition of the Schiffbase to the titanium alkoxide mediated
The β-amino alcohol 1b−Ti(Oi-Pr)4 complex has been shown to catalyze the enantioselective cyanosilylation of aldehydes efficiently. In the presence of 5 mol % of 1b−Ti(Oi-Pr)4 complex catalyst, the aromatic, conjugated, heteroaromatic, and aliphatic aldehydes were converted to their corresponding trimethylsilyl ethers of cyanohydrins in 90−99% yields with up to 94% ee under mild conditions.
β-氨基醇1b -Ti(O i -Pr)4配合物已显示出可有效催化醛的对映选择性氰基硅烷化反应。在5摩尔%的1b -Ti(O i -Pr)4络合催化剂存在下,芳族,共轭,杂芳族和脂族醛以90-99%的产率转化为相应的氰醇三甲基甲硅烷基醚,产率最高为94 %ee在温和条件下。
Enantioselective Total Synthesis of the Unnatural and the Natural Stereoisomers of Vittatalactone
of the cucumber beetle. In this context, we developed the asymmetric total synthesis of the aggregation pheromone of A. vittatum, Vittatalactone, to determine its absolute configuration and to further examine the pheromone response in field studies. The synthesis features an enzyme-catalyzed approach toward the deoxypropionate structural motif. A preformed organocopper reagent could then be coupled in
A Unified Strategy for the Stereospecific Construction of Propionates and Acetate-Propionates Relying on a Directed Allylic Substitution
作者:Tomislav Reiss、Bernhard Breit
DOI:10.1002/chem.200901064
日期:2009.6.22
Flexible friends: A new strategy that relies on o‐DPPB‐directedallylicsubstitution has been implemented for the flexible and stereospecificconstruction of major polyketide and isoprenoid structural elements (see scheme; o‐DPPB=ortho‐diphenylphosphanyl benzoate; PG=protecting group).
α,β-unsaturated (S)-cyanohydrins derived from 2-propenal, 2-butenal, (E) and (Z)-2-hexenal and 2-hexynal are obtained in high enantiomeric purity (80–95% e.e.) by using an oxynitrilase isolated from the leaves of Hevea brasiliensis.